Sleep Cycle Calculator
Suggested bedtimes from a wake time, or suggested wake times from a bedtime — both built on 90-minute sleep cycles + a fall-asleep buffer.
Result
Try going to bed at
21:45 / 23:15 / 00:45 / 02:15
Target wake: 07:00. 15-min fall-asleep buffer.
- 6 cycles (9h sleep)21:45
- 5 cycles (7.5h sleep)23:15
- 4 cycles (6h sleep)00:45
- 3 cycles (4.5h sleep)02:15
Step-by-step
- Sleep happens in ~90-minute cycles (light → deep → REM).
- Waking at the END of a cycle feels easier than mid-cycle.
- Subtract multiples of 90 min from wake time, plus 15 min to fall asleep.
How to use this calculator
- Enter target wake time.
- Adjust fall-asleep time if you tend to lie awake longer.
- Pick the bedtime closest to your usual schedule.
About this calculator
Sleep happens in ~90-minute cycles (Carskadon & Dement, NREM/REM staging). Waking at the end of a cycle (after 4.5, 6, 7.5, or 9 hours of sleep) feels less groggy than waking mid-cycle. Mode 1 subtracts cycles back from your target wake time; mode 2 adds cycles forward from your bedtime. Both account for the time it takes to fall asleep (sleep latency, typically 10-20 minutes per the American Academy of Sleep Medicine).
Frequently asked
It's an average. Real cycles vary 70-110 minutes between people. The calculator uses the population average.
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